This invention pertains to the art of load support or bearing equipment and more particularly to bearing plates of the type adapted to provide support for a generally planar surface.
The invention is particularly applicable to a mine roof bearing plate and will be described with particular reference thereto. However, it will be appreciated by those skilled in the art that the invention has broader applications and may be used in other environments where bearing plates of this general type are deemed necessary and/or desirable.
In underground mining operations of the type where a mine shaft is dug or gouged into the earth for mining purposes, it is necessary to support the roof of the shaft so that it will not cave in and ruin the mining operation with attendant equipment destruction and possible loss of human life. Originally, roofs of coal mine shafts and the like were supported by large wood timbers that extended generally transverse of the entire shaft between the side walls at periodic longitudinal intervals therealong. To provide the necessary support, these timbers or beams were usually rather thick, that is 8 inches or more. Subsequently, it was found unnecessary to have these timbers extend across the entire mine roof to obtain acceptable roof support so that the individual supporting timbers could be shortened somewhat although the thickness thereof remained the same. The substantial beam thickness required was extremely undesirable in that they tended to reduce the effective mine roof or ceiling height.
As mining technology progressed, it was found desirable to utilize a substitute for the wooden support beams to increase or raise the effective mine roof or ceiling height. In addition, more stringent governmental regulations pertaining to mines and mine safety have been enacted which now require very specific mine roof support installations before the digging or construction of a mine shaft may even be commenced. Present regulations now require that specific plans for supporting any newly proposed mine shaft be approved prior to the time that any construction is undertaken. With such closer scrutiny of mining operations, the original wood supports have been variously replaced with supports which are stronger, have a reduced thickness and which normally have longer useful lives.
The present technology for constructing mine shafts is such that a special digging or gouging machine is utilized to dig an approximately 3 feet high initial shaft which is subsequently enlarged to the final desired dimensions. This digging process is continuous and is normally conducted directly through the vein of coal, ore or the like to be mined. The roof of the initial shaft is normally comprised of the material itself which is to be mined with the earth's strata disposed adjacent to and outwardly from this material. As digging of the initial shaft proceeds, the roof supports are immediately installed pursuant to the prior approved plans thereof.
The original wooden or timber supports were first replaced by flat steel plates which were individually mounted to the mine roof itself at periodic designated relative lateral and longitudinal intervals by means of elongated roof bolt members which passed through the plates and into the roofs themselves. These steel plates were originally at least 0.375 inch thick and were fairly expensive so that additional costs were added to the shaft construction. Moreover, this size and type of plate is rather heavy and was found very difficult to work with. When roof plates are first installed, there is a very limited area in which to work and the elongated roof bolts employed to affix the plates to the mine roof are sometimes as long as 10 feet. Under such conditions, the weight of these original plates became far more significant and troublesome than might otherwise seem to be the case.
For the past several years, there has been a trend in the mining industry toward the use of thinner plates now commonly referred to as roof bolt bearing plates in order to reduce the cost, weight and installation problems. The improvement made was to employ steel having a thickness of approximately 0.250 inch and to form the plates so as to have embossed areas which increase the structural rigidity thereof. The use of these thinner plates has been justified by the assumption that they may be made at least as strong as the thicker plates by merely embossing them. The structural rigidity of mine roof bolt bearing plates must meet certain governmental specifications and standards. The standards prescribe that the plates may deflect only certain amounts when supporting designated loads.
While there have been a number of prior designs for these embossed mine roof bearing plates, those which have been most readily accepted as meeting governmental standards have taken one of two primary design configurations, that is, the so called "bell-type" and the "donut-type". The "bell-type" is embossed in a manner such that a cross-section thereof looks very much like a flattened bell and the "donut-type" is embossed in a manner such that a portion thereof taken in cross-section looks very much like a donut.
The present invention contemplates a new and improved bearing plate particularly adapted for use as a mine roof bolt bearing plate which overcomes all of the above referred to problems and others and which provides a bearing plate which is simple in design, economical to manufacture and utilize, facilitates effective support for a larger surface area of a roof, provides means to conceal the head of the mine roof bolt itself, provides means for reducing structural damage to the plate occasioned by accidental contact from mine equipment and machinery and which is readily adapted to use in a plurality of environments.